A “speaker” generates sound from an electrical signal. In the hearing aid art, one often encounters the term “receiver” for such a device, which reads strangely to the uninitiated. “Electroacoustic transducer” is clumsy and pedantic. Thus, “speaker” is the term used for describing this invention.
A human ear canal is a narrow, irregular, tubular structure, approximately 25 mm in length and 7 mm. (0.28 inches) or more in diameter. Coupling amplified sound to the eardrum at the inner end of the canal is not as simple as it might, seem. In a hearing aid, a microphone is connected to a speaker by a high gain (60-80 dB) amplifier and is relatively close to the speaker. Feedback is a problem, much less so in a behind-the-ear (BTE) hearing aid that separates the microphone and the speaker by both distance and the tissue of the outer ear.
Hearing aids can be divided into four groups: Behind-The-Ear (BTE), In-The-Ear (ITE), In-The-canal (ITC), and Completely-In-the-Canal (CIC). It has long been known that putting the speaker in the ear canal reduces feedback in a BTE hearing aid. See “Reducing Feedback in a Post-Auricular Hearing Aid by Implanting the Receiver in an Earmold”, Ross and Cirmo, The Volta Review, January 1980, pages 40-44. (Post auricular means behind the ear). See also U.S. Pat. No. 4,727,582 (de Vries et al.). As Dr. Ross noted in the July/August, 2006, issue of Hearing Loss, “Ironically, some of the very first generation of BTE hearing aids included an external button receiver, simply because there was insufficient room for a receiver in the hearing aid case itself.” Putting a speaker in the ear canal is not so much a hearing aid innovation as a credit to the speaker manufacturers for making their products ever smaller. As Dr. Ross noted in the same article, “because the receivers are now so small, it is possible to also obtain the acoustic advantages of an open ear fitting” with a speaker in the ear canal.
Occlusion and feedback are opposed considerations. Feedback is fairly well defined and can be controlled mechanically and electronically. Occlusion reduces feedback. Occlusion produces the sensation that the ear is plugged, making speaking, chewing, or brushing ones teeth seem very loud. Occlusion is subjective; e.g. U.S. Application Publication 2005/0078843 (Bauman) reports an experimental error of 5-11 dB for insertion effect and more than approximately 3-8 dB for occlusion effect.
Occlusion is treated inconsistently in the prior art. For example, some patents disclose that vents do not prevent occlusion while other patents disclose that vents are effective. Some patents split the difference and say that occlusion depends upon the size of the vent. Other patents express occlusion as a percent. “If the external ear canal . . . is sufficiently open (approximately 50 percent), the ear canal resonance is unchanged and the wearer reports normal sound quality;” U.S. Pat. No. 6,048,305 (Bauman et al.).
U.S. Pat. No. 6,473,513 (Shennib et al.) discloses that occlusion in minimized by placing a “sealing retainer” as far into the canal as practical and provides a gap between the body of a hearing aid and the ear canal to prevent occlusion. The sealing retainer contains a speaker that is electrically coupled to the body of the hearing aid. Whether because of a vent, a gap, or a loose fitting, it is known in the art that occlusion is minimized with an “open” canal.
A host of ear tips have been proposed in the art for locating a tube or a speaker in the ear canal. Variously identified as umbrella, mushroom, dome, jellyfish-shaped tips, such tips have been known in the art for a long time, e.g., U.S. Pat. No. 2,939,923 (Henderson). Plural, dome-shaped tips on a single speaker are disclosed in U.S. Pat. No. 5,887,070 (Iseberg et al.).
Tips are made of a resilient, compliant material and therein lies a problem. Removing the tip often causes the tip to invert in the ear canal, somewhat like an umbrella in a high wind. This can be uncomfortable for the user. U.S. Pat. No. 7,113,611 (Leedom et al.) discloses ribs between the skirt of an ear tip and the stem of the ear tip for preventing inversion. Although effective, the ribs stiffen the tip. High compliance also permits migration of the tip in the canal, which can cause occlusion and further annoyance.
Another problem with tips is the accumulation of debris, notably ear wax, especially if the ear canal is not open. A variety of techniques have been proposed, including tiny filters, to prevent debris from entering the opening for allowing sound to emerge from the tip. The accumulation of debris remains a problem.
In view of the foregoing, it is therefore an object of the invention to provide an ear tip for a hearing aid that minimizes occlusion
Another object of the invention is to provide a tip for a hearing aid that reduces the accumulation of debris.
A further object of the invention is to provide limited, compliant support for the flared portion of a dome-shaped ear tip.